Circumscribed labyrinthitis, also known as labyrinthine fistula, is typically caused by cholesteatoma or granulation tissue eroding the bony labyrinth, resulting in the formation of a fistula. This creates a pathological communication between the middle ear and the membranous labyrinth or perilymphatic space.
Pathology
The inflammatory process leads to localized defects in the bony wall of the vestibule or semicircular canals, mostly the lateral semicircular canal. The bony labyrinth membrane remains intact, and the fistula does not communicate with the perilymphatic space. When the area is exposed to inflammatory or physical stimuli, vertigo symptoms may occur. If the inflammation progresses and the bony labyrinth membrane is destroyed, the fistula may communicate with the perilymphatic space, leading to serous labyrinthitis. If the fistula is located near the promontory, the inflammation may spread and progress to diffuse labyrinthitis. If middle ear inflammation is controlled, and the pathological lesion is removed, the labyrinthitis may resolve, preserving some degree of hearing. Without proper intervention, the condition can progress to suppurative labyrinthitis, forming a dead labyrinth. In rare cases, the fistula may heal spontaneously through new bone formation.
Clinical manifestations
A history of otitis media or middle ear cholesteatoma is present.
Paroxysmal or secondary vertigo is occasionally accompanied by nausea and emesis. The affected labyrinth is in a stimulated state, with the fast phase of spontaneous nystagmus directed toward the affected side. Brief episodes of vertigo may be triggered by pressure changes in the ear canal, such as during ear cleaning, tragus compression, and nose blowing, which is diagnostically significant.
Figure 1 Fistula of the right lateral semicircular canal
Initially, conductive hearing loss is present. In long-standing cases or when the fistula is located near the promontory, mixed hearing loss may occur.
Positive fistula test (vertigo or nystagmus induced by pressure changes in the ear canal) can be seen. If the fistula is blocked by granulation tissue or other lesions, the test may be negative.
Alterations in vestibular function can be observed.
Treatment
During acute episodes, antibiotics in combination with intravenous dexamethasone can be administered. Sedatives may be used as needed. Adequate rest should be ensured.
Surgery should be performed when there is no acute infection. The lateral semicircular canal prominence and the medial wall of the tympanic cavity for fistulas should be inspected carefully. During removal of pathological tissue, disturbing the fibrous connective tissue within the fistula should be avoided to prevent the spread of infection and progression to diffuse labyrinthitis. After debridement, the fistula opening can be covered with temporalis fascia.